Spectrometers having either a prism or a grating as a spectral dispersing element are known. Both prism and grating spectrometers require that relay optics be provided within the system. The inclusion of such relay optics has an adverse effect on the size and on the mass and stability of the system. In general, the spectral stability and accuracy of such systems are compromised by the mechanical sensitivity of the prism or grating and associated relay optics. Such an adverse effect on system size, mass and stability is particularly disadvantageous for portable spectrometers, such as spectrometers intended for mobile and spaceborne applications. In such portable applications the vibration and motion of a platform, in conjunction with the large size and mass of the spectrometer, may render the spectrometer unusable for its intended purpose.
Another type of spectrometer is an interferometer. The use of conventional interferometers is also attended by several problems. In general, these problems with known interferometers are characterized as including precision moving parts, non-simultaneous wavelength acquisition and severe signal processing constraints.
In U.S. Pat. No. 3,442,572 Illsley et al. disclose a wedged filter which is deposited in a circular path around a substrate having a diameter of 6.4 centimeters by the use of two rotating sector masks or by a rotating substrate and a rotating mask in conjunction with a stationary sector mask. The rotating elements have a 2:1 angular velocity ratio. This wedged filter is relatively large, its circular shape may be unsuitable for many applications and the required tooling to fabricate the filter is complex.
It is thus one object of the invention to provide for a wedge filter having a simplification of manufacturing tooling.
It is a further object of the invention to provide a wedge filter having a linear wedge.
It is a further object of the invention to provide a linear wedge filter of small size and mass.
It is still one further object of the invention to provide a wedge filter which may be advantageously integrated with an orthogonally patterned detector array.